Apparatus for purifying metals by pouring through slag

ABSTRACT

Apparatus for the continuous purifying or refining and casting of metals, notably copper, by pouring a metal fused outside the slag layer through the slag layer.

[50] FieldofSearch............................................ 164/52, 82, 252, 281; 13/9; 266/34 R, 34 T, 37; 75/46, 53-57, 61, R, 10A, 10C, 10 P, 10V

[ 5 6 References Cited UNITED STATES PATENTS lnventor Franz Sperner l-lanau/Mair, Germany 7,121 Jan. 30, 1970 Patented Dec. 14, 1971 Assignee Leybold-l-leraeus Verwaltung GmbH 23 wwmmxm /4 w Mm 77 mm .m "n U "v um "0 e..." "k mm m T S eSO .mmdumw kPu k ppmw s oo roo HKSAHV 508480 423347 999999 HHHHHH 7 7477 922609 0006275 074559 85254 2 2 23 y n a m r e G M m .9 W6 2 1 mw n 2 M m r 8" CMGP ll] 23: 333 [ll United States Patent 21 AppLNo.

[22] Filed Primary Examiner-Gerald A. Dost Attorney-Joseph F. Padlon ABSTRACT: Apparatus for the continuous purifying or refining and casting of metals, notably copper, by pouring a metal fused outside the slag layer through the slag layer.

266/34 R, 164/52, l64/252 C21c 7/00 [54} APPARATUS FOR PURIFYING METALS BY POURING THROUGH SLAG 8 Claims, 1 Drawing Fig.

APPARATUS FOR PURIFYING METALS BY POURING THROUGH SLAG This invention relates to an apparatus for purifying metals, particularly copper, upon underslag castings or by pouring a metal fused outside the slag layer through the slag layer.

It is well known to melt metal under a slag layer from one or more consumable electrodes which extend into the slag layer. These methods require that the electrodes be first prepared by casting or welding. it is cumbersome and expensive so to prepare consumable electrodes, and the melting process is particularly uneconomical because of the necessity of providing and removing large amounts of energy (heat of fusion). Furthermore, the necessary apparatus also contributes greatly to the cost. Ultimately, the use of consumable electrodes makes it difficult to arrive at a continuously operating smelting process.

A vacuum electric-arc melting apparatus suitable for continuous operation has become known from German Pat. No. 1,046,212. This device, however, does not avoid the disadvantage inherent in the repeated supply and removal of large amounts of energy in the individual stages of the melting process.

It is known from German published application No. 1,280,508 to melt metal'outside of a slag layer, and to cast the metal through the slag layer to form a block. in order to keep the slag and the metal at the necessary high temperature, the stream of poured metal is enveloped by a hollow, cylindrical electrode. Such known method is not suitable for continuous operation because the hollow electrode does not store enough energy to compensate for the batchwise addition of liquid metal. Moreover, the flowing metal, being dropped from a substantial height, penetrates the slag layer fairly rapidly, thereby making it impossible for the slag and metal to be well mixed as would be necessary for a good purifying effect.

It is an object of the instant invention to overcome the shortcomings of the known devices, and to provide apparatus for purifying metals which is particularly suitable for copper. According to the invention, it will be noted that at the beginning of the melting process, either in a crucible or a continuous casting mold wherein the bottom thereof is at such time closed by a water-cooled dish, a suitable ignition material such as steel wool or a mixture of the same with slag powder is deposited beneath the electrode. Also, the ignition material is surrounded by granular slag. This, being in contact with an electrode, is ignited, whereupon the resultant heat melts the slag and metal. Furthermore, in accordance with the present invention, at least one hollow electrode constituting a collection vessel is arranged above the puddle of molten slag, and its bottom portion is provided with apertures for the discharge of the melt, the bottom portion dipping into the slag layer which is provided above the block of remelted metal which serves as the counterelectrode.

The apparatus of the invention combines several advantageous features. it is not necessary to prepare consumable electrodes of any specific configuration. The metal to be purified may be used as a starting material in any available form, for example, as scrap, and there is no need to solidify the metal after it is molten and prior to purification. Because the stream of molten metal is divided into partial streams which enter the slag layer, there is intimate contact between the metal to be purified and the slag layer, with a high purification effect. Preferably, the metal passes through the slag layer while in the form of drops. Because the molten metal is divided into partial streams only at the slag surface, the kinetic ene gy f th metal entering the slag layer is low. The velocity of the metal in the slag is therefore low, and the dwell time is relatively long. Because the collection vessel is used as one electrode, and the lower block of remelted metal is used as the counterelectrode, the entire slag layer, which extends between the two electrodes, constitutes a resistance heater which is heated to a high temperature. It is in this zone in which the drops of molten metal pass so that the thermal energy is supplied where it is most advantageously used for the metallurgical requirements of the process.

When the hollow electrode of the invention and its discharge openings are suitable dimensioned, the actual pouring process can be made continuous even if the molten metal is received intermittently from a preliminary melting vessel. The apparatus of the invention is thus particularly useful for the continuous casting of metal.

A preferred embodiment will be described herein in greater detail with reference to the sole figure of the attached drawing which shows an apparatus according to the invention in fragmentary elevational section together with supplemental devices.

A premelting furnace 1 may be a so-called "Asarco furnace if copper is to be melted. Electrolytic copper is melted in the furnace in a slightly reducing atmosphere. The mode of operation of such a furnace is usually quasi-continuous. The premelted metal is discharged from the spout or nipple 2 into an intermediate ladle or collecting unit 3. This ladle may be dispensed with, however, even when a discontinuously operated premelting furnace is used. However, its use facilitates the control of the purification process. The intermediate ladle also'permits addition agents to be added and mixed intimately with the molten metal.

The metal melt 5 enters the hollow electrode 6 which constitutes a collecting vessel, from a nipple or spout 4 of ladle 3. Electrode 6 may consist of graphite or a similar, electrically conductive material. It is possible to make the hollow electrode double-walled, and to provide liquid cooling. The hollow electrode illustrated consists of a substantially cylindrical upright wall 7 and a bottom 8 which is provided with several apertures 9. The apertures are uniformly distributed over the area of the bottom wall 8, but as few as two apertures may be adequate. It is also conceivable to place the apertures 9 in the lower end of the upright wall 7, and to immerse the hollow electrode 6 in the slag layer 10 somewhat deeper than is shown in the drawing. As is evident from the drawing, the internal capacity of the hollow electrode is sufficient to permit continuous formation of the block 13 of remelted metal even without the intermediate ladle 3 and with a premelting furnace l which operates batchwise.

Necessary energy is supplied to the hollow electrode 6 by means of a conductor 11 connected to a current source 12. The block 13 made from the molten metal is located below the hollow electrode 6 and is a continuously cast body of uniform cross section in the instant case. At the upper end of the block 13, there is located a puddle 14 of molten metal in which the partial streams of molten metal are consolidated. The block 13 of remolten metal constitutes the counterelectrode for the hollow electrode 6, and is therefore connected with the same current source 12 by means of contact rollers 15 and a conductor l6.

Block 13 with the puddle of melt 14 as well as hollow electrode 6 and slag layer 10 between the electrodes are enveloped by a liquid-cooled mold 17 as is conventional in this art. Said mold contains water 18 as a cooling medium. The drawing shows that the molten metal 5 is discharged through apertures 9 in bottom 8 of the hollow electrode 6 in fine streams which disintegrate into individual drops. The drops travel through slag layer 10 because of their greater specific gravity at a relatively low velocity, thereby permitting intensive interaction and thus effective purification by the slag.

When copper is to be treated, it is most advantageous to make the hollow electrode 6 of graphite because copper does not tend to form carbides, and copper oxide is reduced to copper by the graphite at the prevailing temperature. it is therefore particularly advantageous for this reason to use a graphite-bearing slag.

When the hollow electrode 6 is suitable modified, it is possible to dispense with both the intermediate ladle 3 and the premelting furnace 1. [n this case, the metal to be remelted, for example, scrap, is entered directly into the hollow electrode 6 and fused there. A combination of the feed methods indicated above is also contemplated. In one such modification, only a portion of the metal to be remelted, for example, alloying constituents, is fed directly to the hollow electrode in solid form, whereas the remainder of the metal is drawn from a premelting furnace. Fusion of the scrap in the hollow electrode is facilitated when the electrode has a high-electrical resistivity and thus contributes to the development of thermal energy. Graphite is a suitable electrode material in this case as well.

It is to be noted that the apparatus of the invention can be readily modified to provide the same advantages when operated with polyphase alternating current. When threephase current is used, the single illustrated hollow electrode is merely replaced by three electrodes of the same type which dip into a common slag layer.

lclaim:

1. An arrangement for the continuous purification of metal comprising, in combination, a substantially hollow electrode with bottom wall and sidewalls, said bottom wall having at least two perforations therethrough; means for containing molten slag in proximity of said bottom wall. said perforations discharging into said slag; means for discharging metal into the hollow interior of said electrode; a metal member beneath said slag and in substantially close proximity therewith; and a source of electrical energy connected between said electrode and said member for generating heat within said slag.

2. The arrangement as defined in claim 1 wherein said metal is copper.

3. The arrangement as defined in claim 1 including means for melting said metal exterior to said slag and pouring said molten metal through said slag, a puddle of molten metal fonning at the top of said member, said electrode being above said puddle, said bottom wall with perforations dipping into said slag.

4. The arrangement as defined in claim I wherein said electrode is of material of high-electrical resistivity.

5. The arrangement as defined in claim 4 wherein said material is graphite.

6. The arrangement as defined in claim 1 including cooling means communicating with said electrode and said slag.

7. The arrangement as defined in claim 1 including means for moving said member relative to said electrode.

8. The arrangement as defined in claim 1 including container means for containing said electrode and said slag, said member having a molten metal top and a solid metal bottom, said electrode being of graphite. 

2. The arrangement as defined in claim 1 wherein said metal is copper.
 3. The arrangement as defined in claim 1 including means for melting said metal exterior to said slag and pouring said molten metal through said slag, a puddle of molten metal forming at the top of said member, said electrode being above said puddle, said bottom wall with perforations dipping into said slag.
 4. The arrangement as defined in claim 1 wherein said electrode is of material of high-electrical resistivity.
 5. The arrangement as defined in claim 4 wherein said material is graphite.
 6. The arrangement as defined in claim 1 including cooling means communicating with said electrode and said slag.
 7. The arrangement as defined in claim 1 including means for moving said member relative to said electrode.
 8. The arrangement as defined in claim 1 including container means for containing said electrode and said slag, said member having a molten metal top and a solid metal bottom, said electrode being of graphite. 